<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <input type="text"><button>点击</button>
    <div></div>
    <script>
    // trim 方法去除字符串两侧空格
    var str = '  andy  ';
    console.log(str);
    var str1 = str.trim();
    console.log(str1);

    var input = document.querySelector('input');
    var btn = document.querySelector('button');
    var div = document.querySelector('div');
    btn.onclick = function() {
        var str = input.value.trim();
        if (str === '') {
            alert('请输入内容');
        } else {
            console.log(str);
            console.log(str.length);
            div.innerHTML = str;
        }
    }
    </script>
</body>
</html>